1. Technical Field
The present invention generally relates to protection of disk drives such as a Redundant Array of Independent Disks (xe2x80x9cRAIDxe2x80x9d) storage system from external and/or internal mechanical disturbances. The present invention especially relates to the use of viscoelastic foam materials to protect arrays of disk drives from such disturbances. It is of course well known that foams can provide a wide variety of damping and compliance characteristics. These characteristics generally follow from the fact that foams contain long-chain molecules that are capable of converting mechanical energy into heat when the foam is deformed.
2. Description of Related Art
Since RAID storage systems are one of the most important forms of disk drive arrays, they will be used to illustrate and differentiate applicant""s invention. Generally speaking, RAID storage systems are arrays of disk drives (xe2x80x9cDDsxe2x80x9d) controlled by one or more controllers. Higher data transfer rates are achieved through the ability of the system""s controller to schedule, read and write commands to multiple DDs in a parallel fashion. Such storage systems employ one or more motor driven spindles that rotate the DDs at several thousand revolutions per minute. Such systems also have a printed circuit board that receives commands from the controller and translates them into voltage fluctuations that cause a head actuator to move an array of ganged read/write heads across a complimentary array of disks. The head actuator must push and pull each gang with the extreme precision required to properly position a given head with select tracks that lie in concentric circles on the surface of a disk being served by that head. In short, disk drive systems are very precise, and very delicate, pieces of equipment that must be protected from mechanical shocks and vibrationsxe2x80x94from whatever source.
Therefore, owing to their mechanical sensitivities, these systems are shipped to their end users in external packaging systems that include extra and/or specifically designed, and hence expensive, foam padding systems. Those skilled in the disk drive arts also will appreciate that a RAID system""s DDs are especially susceptible to external mechanical disturbances. Consequently, these DDs are shipped separately from the rest of the RAID system. The individual DDs are usually placed in compartmentalized, foam-lined, boxes and static electricity resistance bags. Aside from its greater packaging and shipping costs, this practice also adds a great deal to the setup time when a RAID system is unpacked and installed.
Aside from carefully packing their products for shipping in external foam padding systems, RAID system manufacturers also have provided compliant mounting systems for individual DDs in order to protect them from external mechanical disturbances during use of the RAID system. For example, some manufacturers have followed the practice of placing a complaint medium between each DD and the enclosure cage to which the individual DDs are mounted. These DDs are mounted to their enclosure cage in this compliant manner in order to filter potentially harmful external mechanical disturbances. Unfortunately, a RAID""s throughput performance can be diminished as a result of this type of compliant mounting of individual DDs to their DD enclosure cage. That is to say that, under the compliant mounting conditions between the individual DDs and the DD enclosure cage, the DDs may exhibit diminished throughput performance due to certain self-induced vibrations which the compliant mountings permit to occur. For example, under these compliant mounting conditions, servomechanism movements of individual DDs can cause rotational vibration disturbances that can cause one or more DDs in a DD array to become self-disturbed or self-excited. It is also possible for DDs to be adversely affected by translational forces from external sources after they are placed in operation.
It therefore would be very advantageous to (1) protect arrays of disk drives such as those employed in RAID systems from external mechanical disturbances during shipping, (2) ship such systems with their DDs preinstalled in order to decrease installation costs and (3) protect such systems from internal and external vibrations and/or mechanical shock during operation. Accomplishing these ends by use of a single, permanently installed, mechanical means is a particularly desirable circumstance. Applicant has found that these advantages can be obtained through at least two distinct means: employment of foams in certain mechanical disturbance damping systems hereinafter more fully described, and/or by mounting disk drives to their enclosure cage in as rigid a fashion as possible.
Applicant has found that external mechanical disturbances to disk drive arrays, and especially hard disk drive arrays (e.g., RAID systems employing arrays of hard disk drives), during shipping, installation and use, as well as self-excitation of such disk drives (xe2x80x9cDDsxe2x80x9d) as a result of their operation, all can be filtered or attenuated by the hereindescribed foam systems. These foam systems also may allow such DDs to be shipped preinstalled, thereby eliminating the current need for extensive, and hence costly, unpacking and installation operations.
To achieve these ends, applicant provides a disk drive enclosure system, comprising: an enclosure, a cage configured to mount a plurality of disk drives and foam between the cage and the enclosure. Generally speaking a plurality of disk drives are mounted to the cage. Thus, applicant""s disk drive enclosure system has a viscoelastic foam on at least one outside surface of a DD array and/or an enclosure cage to which that DD array is mounted. For the purposes of this patent disclosure, this combination of a DD array and an enclosure cage to which the array is mounted will often be referred to as a xe2x80x9cDD/enclosure cage assemblyxe2x80x9d. This DD/enclosure cage assembly can be provided with one or more layers of foam at various places on that assembly. The resulting DD/enclosure cage assembly/foam system is then placed inside an enclosure which, in turn, is mounted in an external housing.
In some embodiments of this invention, the foam is placed in a state of compression between the DD/enclosure cage assembly and the enclosure. This compressed state can follow from the fact that a given piece of foam, in its uncompressed state, is thicker than the space into which it is inserted. Upon being compression fitted into the space between the enclosure and the DD/enclosure cage assembly, the foam naturally presses outwardly against both the enclosure and the enclosure cage assembly. Thus, the foam materials used in the practice of this embodiment are preferably resilient as well as compressible.
In some of the more preferred embodiments of this invention, the DDs also will be rigidly mounted to the DD enclosure cage. For the purposes of this patent disclosure, applicant""s use of the expression xe2x80x9crigidly mountedxe2x80x9d can be taken to mean that no foam or other compliant material is placed between the individual DDs and the DD enclosure cage, e.g., as they are in the prior art DD mounting practice previously noted. That is to say that under applicant""s rigid mounting conditions, a plastic (or metal) housing of an individual DD will normally be pressed directly against a metal (or plastic) enclosure cage element. The resulting rigid mounting raises the effective inertia of the entire DD arrayxe2x80x94and thereby reducing its self excited dynamic responses. This rigid mounting practice also serves to reduce the natural frequency of applicant""s DD arrays. The resulting lower frequencies will serve to attenuate higher, more harmful, frequencies (which include shock) that may be directed toward the DD array. In other words, very little force and/or torsion will be transmitted to the DDs when applicant""s DD/enclosure cage assembly is provided with a low natural frequency by rigidly mounting the DDs to the enclosure cage.